The present invention relates to universal joints, and more particularly to a universal joint which is called a ball joint and which is suitable for connecting an input shaft to an output shaft, for example, for use in vehicle steering mechanisms.
FIGS. 19 to 21 show a known universal joint of this type (see Unexamined Japanese Utility Model Publication SHO 59-122430).
The illustrated universal joint consists essentially of a substantially spherical intermediate joint member 10 made of synthetic resin and two metal shafts 11 and 12.
The first shaft 11, which is to be disposed at the drive side, has a first arm 13 and a second arm 14 projecting from its forward end in a bifurcated fashion. These two arms 13, 14 are trapezoidal in cross section, and are generally U-shaped in combination, resembling a partially cut-out circle. The inward opposed faces of the two arms 13, 14 form a segment of a spherical surface. The second shaft 12, which is to be disposed at the driven side, has a forward end bifurcating into a third arm 15 and a fourth arm 16 as in the case of the first shaft 11. The second shaft 12 is formed between its two arms 15, 16 a recess 17 for passing the arms 13, 14 of the first shaft 11 therethrough when the parts are assembled.
The intermediate joint member 10 as assembled comprises a spherical portion 18 and first to fourth four ridges 19, 20, 21 and 22 formed externally on the portion 18 and equidistantly arranged circumferentially thereof. The first and second ridges 19, 20 are arranged symmetrically about the center of the portion 18, and the third and fourth ridges 21, 22 are also arranged symmetrically as spaced from these ridges by 90 degrees about the center. The first and third ridges 19, 21 define a first guide furrow 23 therebetween, and the second and fourth ridges 20, 22 symmetrical with these ridges define a second guide furrow 24 therebetween. The third and second ridges 21, 20 define a third guide furrow 25 therebetween, and the fourth and first ridges 22, 19 symmetrical with the ridges 20, 21 define a fourth guide furrow 26 therebetween.
The entire intermediate joint member 10 is divided into first and second two divided half joint segments 10a, 10b arranged axially thereof. The first segment 10a comprises a first spherical half segment 18a obtained by dividing the spherical portion 18 into two equal portions, and first half portions 19a, 20a, 21a and 22a of the four ridges 19, 20, 21 and 22 integrally formed on the outer surface of the spherical half segment 18a. The second joint member half segment 10b comprises the other half of the spherical portion 18, i.e., a second spherical half segment 18b, and second half portions 19b, 20b, 21b and 22b of the four ridges 19 to 22 integrally formed on the outer surface of the spherical half segment 18b. The two half segments 10a, 10b are combined with their cross-shaped inner faces 27a, 27b opposed to each other to form the joint member 10 which is substantially spherical. The combination faces 27a, 27b of the joint half segments 10a, 10b are formed with spring accommodating cavities 28a, 28b, respectively, having a U-shaped metal spring 29 fitted therein. The spring 29 provided between the bottoms of the cavities 28a, 28b has opposite ends 29a slightly projecting into the first and fourth guide furrows 23, 26 at opposite sides of the first ridge 19.
The first arm 13 of the first shaft 11 is fitted in the first guide furrow 23 of the joint member 10, and the second arm 14 thereof in the second guide furrow 24. The third arm 15 of the second shaft 12 is fitted in the third guide furrow 25 of the joint member 10, and the fourth arm 16 thereof in the fourth guide furrow 26. The spring ends 29a projecting into the first and fourth guide furrows 23, 26 are in pressing contact with the first arm 13 and the fourth arm 16, thereby precluding backlashing.
The rotation of the first shaft 11 is transmitted to the second shaft 12 through the intermediate joint member 10. In the case of forward rotation, the arms 13, 14, 15, 16 of the two shafts 11, 12 are in contact with the ridges 19, 20 of the intermediate joint member 10 at four locations for power transmission. In the case of reverse rotation, the arms 13, 14, 15, 16 are in contact with the ridges 21, 22 at other four locations, whereby the power is transmitted. More specifically stated, when the first shaft 11 is rotated forward as indicated by an arrow X in FIG. 21, a side face 13a of the first arm 13 of the first shaft 11, i.e., the forward side thereof with respect to the direction of forward rotation, pushes the rearward side face, with respect to the direction of forward rotation, of the first ridge 19; the forward side face 14a, with respect to the direction of forward rotation, of the second arm 14 pushes the rearward side face, with respect to the direction of forward rotation, of the second ridge 20; the forward side face, with respect to the direction of forward rotation, of the first ridge 19 pushes the rearward side face 16a with respect to the direction of forward rotation, of the fourth arm 16; and the forward side face, with respect to the direction of forward rotation, of the second ridge 20 pushes the rearward side face 15a, with respect to the direction of forward rotation, of the third arm 15. Consequently, the second shaft 12 is rotated in the same direction as the first shaft 11. Further when the first shaft 11 is rotated reversely as indicated by an arrow Y in FIG. 21, the forward side face 13b, with respect to the direction of reverse rotation, of the first arm 13 of the first shaft 11 pushes the rearward side face, with respect to the direction of reverse rotation, of the third ridge 21; the forward side face 14b, with respect to the direction of reverse rotation, of the second arm 14 pushes the rearward side face, with respect to the direction of reverse rotation, of the fourth ridge 22; the forward side face, with respect to the direction of reverse rotation, of the third ridge 21 pushes the rearward side face 15b, with respect to the direction of reverse rotation, of the third arm 15; and the forward side face, with respect to the direction of reverse rotation, of the fourth ridge 22 pushes the rearward side face 16b, with respect to the direction of reverse rotation, of the fourth arm 16, whereby the second shaft 12 is rotated in the same direction as the first shaft 11.
With the universal joint described above, the two shafts 11, 12 are moved along the guide furrows 23, 24 and 25, 26 in the joint member 10, whereby the angle (operation angle) between the two shafts 11, 12 is variable as desired. However, when an operation angle is given, the rotation of the shafts 11, 12 reciprocatingly moves the arms 13, 14, 15, 16 in directions along the guide furrows 23, 24, 25, 26 relative to the joint member 10, whereby the opposite ends 29a of the spring 29 are reciprocatingly moved on the arms 13, 16 in pressing contact therewith. Since the spring 29 thus slidingly moves on the arms 13, 16 relative thereto in metal-to-metal contact, the spring 29 or the arms 13, 16 undergo marked wear, rendering the spring 29 inoperative as such within a relatively short period of time to permit backlashing.